If you're using HathiTrust seriously and aren't affiliated with a partner library, consider Hathi Download Helper to get complete public domain books archived to local storage. I wrote an earlier command-line version of the tool. Someone else built a GUI and put in the work to keep up with the evolving API.
I often use Google to locate a book, then check Internet Archive and HathiTrust if it's old enough that it should be public domain under US law. I really appreciate HathiTrust putting in the effort to check copyright renewals and make more of their materials fully visible. I don't appreciate the technical barriers to downloads that they erect, but that's out of the hands of the developers working there. As long as their web viewer shows individual pages you can be sure there will be a way to reassemble full books.
Once I needed a copy of The Congressional Record from the 40's and Google had marked it non-public! I had to make several calls to Hathi to explain that the Record is public by law and then they had to contact Google to get the restriction lifted.
It's a lot of rigamarole for information that researchers need.
I often use Google to locate a book, then check Internet Archive and HathiTrust if it's old enough that it should be public domain under US law. I really appreciate HathiTrust putting in the effort to check copyright renewals and make more of their materials fully visible. I don't appreciate the technical barriers to downloads that they erect, but that's out of the hands of the developers working there. As long as their web viewer shows individual pages you can be sure there will be a way to reassemble full books.